3-Exomethylenecephams are of great value as intermediates in the synthesis of cephalosporin antibiotics. Most recently, 3-exomethylenecepham sulfoxides have been employed to prepare 3-acetoxymethylcephem compounds (U.S. Pat. No. 4,029,651 issued June 14, 1977) and 3-chloro cephems (U.S. Pat. No. 3,925,372 issued Dec. 9, 1975). The demonstrated versatility of 3-exomethylenecephams as intermediates to cephem antibiotic compounds has prompted a continuing investigation into new synthetic routes to these intermediates.
3-Exomethylenecepham intermediates have been prepared from cephalosporanic acids by first treating the cephalosporanic acids with selected sulfur nucleophiles such as thiourea, thiobenzoic acid or potassium ethyl xanthate and then reducing the respective product C.sub.3 -(substituted)-thiomethylcephems with either Raney nickel in aqueous ethanol or zinc in formic acid-dimethylformamide. More recently 3-exomethylenecepham intermediates have been prepared by the acid catalyzed cyclization of certain penicillin sulfoxide derived azetidinone sulfinyl chlorides (S. Kukolja, et al., Journal of the American Chemical Society, 98, 5040 (1976).
This invention relates to the novel preparation of 3-exomethylenecepham sulfoxides by the reaction of 3-halo-3-methylcepham sulfoxides with mercuric or mercurous perchlorate.